UV curable epoxy resin compositions and their uses are well known in the art. Such compositions are used, for example, in printing inks, protective, decorative, and insulating coatings, pitting compounds, sealants, adhesives, molding compositions, wire insulation, textile coatings, laminates, impregnated tapes, varnishes, etc.
One problem with expanding the use of UV curable epoxy resins is that they may only be utilized where UV light can penetrate for curing. Further, upon exposure, cure begins immediately on the exposed surface and progresses into the resin with continued exposure. Thus, there is no opportunity to work the resin after exposure begins. Although, it is possible to cure many of these compositions by heating to temperatures of greater than about 150.degree. C. This is simply impractical in most situations. As a consequence of the above, uses which require a composition to bond two opaque surfaces, to cure in a shaded area, or to be worked after UV exposure are not suitable for the application of UV curable epoxy compositions.
U.S. Pat. No. 4,308,118 discloses the combination of a UV activated and thermally activated catalyst to produce deep section cure epoxy resin compositions. These compositions may contain UV opaque fillers yet cure quickly upon the application of heat and UV radiation.
U.S. Pat. No. 3,960,979 discloses the use of polyether polyols, including polyethylene glycol and polypropylene glycol as flexibilizing agents in heat cured epoxy resins. These epoxy resins utilize an acid catalyst and a bake cycle at temperatures of from 80.degree. C. to about 210.degree. C.
U.S. Pat. No. 4,434,286 discloses the use of polyether polyols as a flexibilizing agent in cycloaliphatic epoxide resins having good electrical properties. These epoxy resin compositions utilize organic acids to catalyze the cure at temperatures of from about 100.degree. C. to about 200.degree. C.
It is an object of the present invention to produce a UV curable epoxy composition that can be worked in an open time following exposure to UV radiation.
It is another object of the present invention to provide a UV curable epoxy composition with a fixed period of cure delay following exposure to UV radiation.